Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session NK: Nuclear Fission I |
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Chair: Shea Mosby, Los Alamos National Laboratory Room: City Center B |
Saturday, October 28, 2017 8:30AM - 8:42AM |
NK.00001: Fission fragment anisotropy of $^{235}$U measured with the fissionTPC David Hensle, Uwe Greife The fissionTPC, built for the purpose of making neutron-induced fission cross section measurements with unprecedented precision, is a two-chamber MICROMEGAS time projection chamber that allows for three-dimensional tracking of charged particles. This three-dimensional tracking capability also provides a direct measurement of fission fragment angular distributions for neutron-induced fission. Fragment angular anisotropy is an important experimental observable for understanding the quantum mechanical state of the fissioning nucleus and a parameter required to determine detection efficiency for cross section measurements. Preliminary results for $^{235}$U fission fragment anisotropy as a function of neutron energies in the range $130$~keV$ - 100$~MeV will be presented. [Preview Abstract] |
Saturday, October 28, 2017 8:42AM - 8:54AM |
NK.00002: Abstract Withdrawn
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Saturday, October 28, 2017 8:54AM - 9:06AM |
NK.00003: Measuring Fission Fragment Mass Distributions as a Function of Incident Neutron Energy Using the fissionTPC Joshua Gearhart Fission fragment mass distributions are important observables for developing next generation dynamical models of fission. Many previous measurements have utilized ionization chambers to measure fission fragment energies and emission angles which are then used for mass calculations. The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) collaboration has built a time projection chamber (fissionTPC) that is capable of measuring additional quantities such as the ionization profiles of detected particles, allowing for the association of an individual fragment's ionization profile with its mass. The fragment masses are measured using the previously established 2E method. The fissionTPC takes its data using a continuous incident neutron energy spectrum provided by the Los Alamos Neutron Science CEnter (LANSCE). Mass distribution measurements across a continuous range of neutron energies put stronger constraints on fission models than similar measurements conducted at a handful of discrete neutron energies. [Preview Abstract] |
Saturday, October 28, 2017 9:06AM - 9:18AM |
NK.00004: Energy Dependence of Fission Product Yields from $^{235}$U, $^{238}$U and $^{239}$Pu for Incident Neutron Energies Between 0.5 and 14.8 MeV Matthew Gooden, Todd Bredeweg, Malcolm Fowler, David Vieira, Jerry Wilhelmy, Anton Tonchev, Mark Stoyer, Megha Bhike, Sean Finch, FNU Krishichayan, Werner Tornow The energy dependence of a number of cumulative fission product yields (FPY) have been measured using quasi- monoenergetic neutron beams for three actinide targets, $^{235}$U, $^{238}$U and $^{239}$Pu, between 0.5 and 14.8 MeV. The FPYs were measured by a combi- nation of fission counting using specially designed dual-fission chambers and -ray counting. Each dual-fission chamber is a back-to-back ioniza- tion chamber encasing an activation target in the center with thin de- posits of the same target isotope in each chamber. This method allows for the direct measurement of the total number of fissions in the activa- tion target with no reference to the fission cross-section, thus reducing uncertainties. γ-ray counting of the activation target was performed on well-shielded HPGe detectors over a period of 2 months post irradiation to properly identify fission products. Reported are absolute cumulative fission product yields for incident neutron energies of 0.5, 1.37, 2.4, 3.6, 4.6 and 14.8 MeV. New data in the second chance fission region of 5.5 - 9 MeV are included. [Preview Abstract] |
Saturday, October 28, 2017 9:18AM - 9:30AM |
NK.00005: Short Lived Fission Product Yield Measurements in $^{235}$U, $^{238}$U and $^{239}$Pu Jack Silano, Anton Tonchev, Werner Tornow, Fnu Krishichayan, Sean Finch, Matthew Gooden, Jerry Wilhelmy Yields of short lived fission products (FPYs) with half lives of a few minutes to an hour contain a wealth of information about the fission process. Knowledge of short lived FPYs would contribute to existing data on longer lived FPY mass and charge distributions. Of particular interest are the relative yields between the ground states and isomeric states of FPYs since these isomeric ratios can be used to determine the angular momentum of the fragments. Over the past five years, a LLNL-TUNL-LANL collaboration has made precision measurements of FPYs from quasi-monoenergetic neutron induced fission of $^{235}$U, $^{238}$U and $^{239}$Pu [1]. These efforts focused on longer lived FPYs, using a well characterized dual fission chamber and several days of neutron beam exposure. For the first time, this established technique will be applied to measuring short lived FPYs, with half lives of minutes to less than an hour. A feasibility study will be performed using irradiation times of $<$ 1 hour, improving the sensitivity to short lived FPYs by limiting the buildup of long lived isotopes. Results from this exploratory study will be presented, and the implications for isomeric ratio measurements will be discussed. [1] M. Gooden et al. Nucl. Data Sheets. 131, 319 (2016) [Preview Abstract] |
Saturday, October 28, 2017 9:30AM - 9:42AM |
NK.00006: Neutron capture cross-section measurements for $^{238}$U between 0.4 and 1.4 MeV Fnu Krishichayan, S.W. Finch, C.R. Howell, A.P. Tonchev, W. Tornow Neutron-induced radiative-capture cross-section data of $^{238}$U are crucial for fundamental nuclear physics as well as for Stewardship Science, for advanced-fuel-cycle calculations, and for nuclear astrophysics. Based on different techniques, there are a large number of $^{238}$U(n,$\gamma$) $^{239}$U cross-section data available in the literature. However, there is a lack of systematic and consistent measurements in the 0.1 to 3.0 MeV energy range. The goal of the neutron-capture project at TUNL is to provide accurate $^{238}$U(n,$\gamma$) $^{239}$U cross-section data in this energy range. The $^{238}$U samples, sandwiched between gold foils of the same size, were irradiated for 8-14 hours with monoenergetic neutrons. To avoid any contribution from thermal neutrons, the $^{238}$U and $^{197}$Au targets were placed inside of a thin-walled pill-box made of $^{238}$U. Finally, the whole pill-box was wrapped in a gold foil as well. After irradiation, the samples were gamma-counted at the TUNL’s low-background counting facility using high-efficient HPGe detectors. The $^{197}$Au monitor foils were used to calculate the neutron flux. The experimental technique and $^{238}$U(n,$\gamma$) $^{239}$U cross-section results at 6 energies will be discussed during the meeting. [Preview Abstract] |
Saturday, October 28, 2017 9:42AM - 9:54AM |
NK.00007: Current estimates of the energy released following the fission of actinide nuclides Alejandro Sonzogni, Elizabeth McCutchan We calculate the energy released following the neutron induced fission of the main fuel nuclides in a reactor, 235U, 238U, 239Pu and 241Pu. These energies are used in a number of fields, but we were particularly motivated by their application in the recent measurements of reactor antineutrinos spectra and yields. The calculations are performed using the best estimates of cumulative fission yields for long-lived fission products and the recently released 2016 Atomic Mass Evaluation by Wang et al. Additionally, we obtain more precise values of the energy taken away by antineutrinos by using the latest Total Absorption Gamma Spectroscopy (TAGS) results. An important part of this project is also to obtain realistic estimates of the uncertainties. A comparison with earlier calculations will be presented. [Preview Abstract] |
Saturday, October 28, 2017 9:54AM - 10:06AM |
NK.00008: Measurement of $^{240}$Pu Angular Momentum Dependent Fission Probabilities Using the ($\alpha,\alpha'$) Reaction Johnathon Koglin, Jason Burke, Scott Fisher, Igor Jovanovic The surrogate reaction method often lacks the theoretical framework and necessary experimental data to constrain models especially when rectifying differences between angular momentum state differences between the desired and surrogate reaction. In this work, dual arrays of silicon telescope particle identification detectors and photovoltaic (solar) cell fission fragment detectors have been used to measure the fission probability of the $^{240}$Pu($\alpha,\alpha'f$) reaction - a surrogate for the $^{239}$Pu($n,f$) - and fission fragment angular distributions. Fission probability measurements were performed at a beam energy of 35.9(2) MeV at eleven scattering angles from 40$^{\circ}$ to 140$^{\circ}$e in 10$^{\circ}$ intervals and at nuclear excitation energies up to 16 MeV. Fission fragment angular distributions were measured in six bins from 4.5 MeV to 8.0 MeV and fit to expected distributions dependent on the vibrational and rotational excitations at the saddle point. In this way, the contributions to the total fission probability from specific states of K angular momentum projection on the symmetry axis are extracted. A sizable data collection is presented to be considered when constraining microscopic cross section calculations. [Preview Abstract] |
(Author Not Attending)
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NK.00009: Prompt Fission Neutron Multiplicities for $^{241}$ Pu using Surrogate Reactions Oluwatomi Akindele, Jason Burke, Robert Casperson, Richard Hughes, Eric Norman, Antti Saastamoinen, Barbara Wang The prompt fission neutron multiplicity for \textsuperscript{241}Pu was measured at the Texas A$\&$M University Cyclotron using the NeutronSTARS array. Due to the short half-life ($14.3$ yrs) of \textsuperscript{241}Pu, inelastic scattering on \textsuperscript{242}Pu with 55 MeV alpha particles was used as a surrogate. The average neutron multiplicity ($\bar{\nu}$), and the neutron multiplicity distribution for equivalent neutron energies up to 20 MeV are discussed and reported. [Preview Abstract] |
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